class Solution5 {

    boolean[][] vis;
    int m, n, step, ret;
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};

    public int uniquePathsIII(int[][] grid) {
        m = grid.length; n = grid[0].length;
        vis = new boolean[m][n];
        int bx = 0, by = 0;

        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(grid[i][j] == 0) { step++;}
                if(grid[i][j] == 1) { bx = i; by = j;}
            }
        }
        vis[bx][by] = true;
        step += 2;

        dfs(grid, bx, by, 1);
        return ret;
    }

    public void dfs(int[][] grid, int i, int j, int count){

        if(grid[i][j] == 2){
            if(count == step) { ret++;}
            return ;
        }

        for(int k = 0; k < 4; k++){
            int x = i + dx[k], y = j + dy[k];
            if(x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] && grid[x][y] != -1){
                vis[x][y] = true;
                dfs(grid, x, y, count + 1);
                vis[x][y] = false;
            }
        }
    }
}